The apparatus disclosed herein was developed to reduce the low speed exhaust noise levels produced by high performance internal combustion engines, while maintaining and improving engine performance levels in lower speed ranges without affecting engine performance at the high speeds for which such engines are designed.
High performance internal combustion engines are utilized in boats, automobiles, trucks, off-road vehicles, motorcycles and other vehicles for recreational and sports usage. Because such engines operate at top speed with greatest efficiency and power when exhaust back pressure is at a minimum, they are typically provided with large open exhaust headers that serve as expansion chambers for the hot exhaust gases. These headers are open to the atmosphere without restrictions that would increase back pressure.
Such engines can be effectively (and legally) operated in some remote areas, where noise levels of engine operation are either not regulated or are environmentally acceptable. However, such areas are becoming more rare as people in increasing numbers have sought recreational and sports activities in more remote and rural areas.
Noise and engine power are closely related, particularly in the minds of enthusiasts owning and operating vehicles powered by large displacement high performance engines. It has been observed that those operating such engines often attempt to emphasize vehicle performance by a high level of intake and exhaust noise. Noise is as often a substitution for speed as a by-product of it. The explanation for the exhilaration provided by high noise levels is that much of the appeal of owning or operating a fast car, motorcycle, or boat is the joy of being noticed. One way to assure such notoriety is to operate a vehicle at such a high noise level that those about the area are forced to take notice of it.
As the numbers of high performance vehicles has increased, the public's tolerance for such noise levels has decreased. Current concern for environmental factors includes concern about noise levels and the effect of noise on quality of life. It has therefore become imperative that operators of vehicles powered by high performance engines modify the engines to make their performance more compatible with current environmental standards.
Most sound-reduction systems result in increased exhaust system restriction and reduced power. Such systems typically involve the use of a muffler or sound disperser. They involve convoluted exhaust paths, baffles and other restrictions which deviate from the unimpeded expansion of exhaust gas necessary for highest engine performance.
As a compromise, many noise reduction systems utilize a "bypass" or "cutout" system. A valve or diverter within the exhaust pipe is manually or automatically operated to allow the user of the engine to mechanically select either straight-through exhaust routing or a path that goes through a noise reduction mechanism. This allows dampening of sound in noise-restricted areas, and straight-through power and sound in open areas where sound restrictions are not encountered. However, such systems are not variable in nature--the bypass is either operative or inoperative at any given stage of engine operation. These systems are also relatively expensive, due to the mechanical linkages and controls required in order to effectively operate such a valve, plus the dual nature of the noise reduction system which must be added to the usual headers. The systems are typically manually operated, and therefore noise reduction is achieved essentially at the whim and control of the engine operator.
The present invention provides automatically varying noise reduction. It results in full noise reduction at idle and low speed engine operation, and essentially unrestricted exhaust flow at high speed engine operation. This variable mode of achieving engine noise reduction is particularly applicable to boats incorporating high peformance internal combustion engines. It has been found that the most controversial problem in the operation of such boats is the high level of noise which they generate while near the dock area or shoreline, particularly as the boats are headed directly out from the shoreline with their exhausts directed rearwardly at those on shore. By providing maximum sound abatement at low speed engine operation, the present invention dramatically reduces the amount of noise projected to shore during initial boat operation. At the same time, the device automatically opens the exhaust outlets during high speed operation of the boat, which typically takes place at a substantial distance from shore. At such times the boat is less likely to be projecting its exhaust noises directly rearward to an identifiable dock or shore area.